This invention relates generally to an improved construction for hot water heaters. These water heaters typically include a storage tank formed as an upright cylinder from steel or ferric metal plate and an anode used to protect the tank from galvanic corrosion. This invention pertains more specifically to a non-sacrificial anode for use in water heater construction which will protect the tank more effectively, efficiently and safely than prior non-sacrificial anodes.
Non-sacrificial anodes generally include one or more elongated filaments of electrically conductive metal impressed with a small electrically positive potential so as to produce direct current from the anode to the metal tank. The current counteracts the corrosive activity of the water and dissolved oxygen to protect the metal tank and fixtures from galvanic corrosion. The voltage of the impressed current is dependent upon, among other things, the quality and characteristics of the lining, the electrical conductivity of the water within the tank, and the configuration of the anode in relation to the tank walls and other metal elements.
Non-sacrificial anodes are deficient in at least two significant aspects. Since the protective current follows the path of least resistance, it will frequently flow directly from the anode to a nearby metal projection, such as the heating elements, leaving the tank walls and remaining fixtures unprotected. It is known to compensate for this limitation by utilizing a higher voltage so that the protective current is applied to all areas of the tank walls and fixtures notwithstanding a relatively greater current drain in some localized area. However, the materials, methods of construction and operating conditions commonly associated with anode and tank are expensive and inherently limited so as to make operation of the tank and non-sacrificial anode system dangerous, especially in certain conditions. The higher voltages associated with certain systems increase the danger.
Expense is related to materials and methods of construction. One conventional type of anode includes a filament of titanium coated with platinum. Use of this type is limited to low voltage systems because the platinum/titanium interfaces break down at voltages above 13 volts. The construction of this type anode generally includes installing the anode as a plurality of short discreet filaments interspaced within the tank in order to avoid proximity between the anode and metal projections within the tank; this requires more materials and labor than single filament systems.
Single filament non-sacrificial anodes are high voltage types of conventional anodes and generally use a tantalum wire coated with platinum as the platinum/tantalum interface will withstand 85 to 100 volts. However, tantalum is more expensive than titanium and the higher voltage increases the dangers associated with non-sacrificial anodes.
The danger associated with non-sacrificial anodes results from an accumulation of hydrogen and oxygen gas generated through the electrolysis of water by the protective current flowing from the anode to the tank and fixtures. The presence of hydrogen and oxygen gas in an enclosed space creates a very real threat of explosion. In normal operating conditions much of the hydrogen and oxygen gases are dissolved in the water flowing through and out of the tank. But when the heater stands idle, as when a homeowner goes on vacation, the static conditions in the tank produce a serious explosion hazard -- so serious that no hot water heater, now commercially available and known to this applicant, has received the safety approval of either governmental or non-governmental consumer safety organizations. It can also be seen that the rate of accumulation of the gases depends primarily upon the magnitude of the protective current. Thus the larger the protective current, the more dangerous the explosion potential. This invention improves upon the conventional non-sacrificial anodes and hot water heaters in all of these respects.